1. Field of the Invention
The present invention pertains to lay-up molds. More particularly, the present invention relates to hybrid lay-up molds. Even more particularly, the present invention concerns molds used in the manufacture of aerospace composite parts.
2. Description of Related Art
As is known to those skilled in the art to which the present invention pertains, the use of carbon fiber (CF) composite material and Invar® alloys in fabricating molds for the manufacture of various aerospace components or parts is well documented. See, inter alia, U.S. Pat. Nos. 6,759,002; 8,511,362; 6,168,358; as well as European Patent No. 0642904 and U.S. Patent Publication Nos. 2009/035412 and 2015/009834.
Molds fabricated from CF composite materials are lighter in weight compared to Invar® molds, and are characterized by a lower thermal mass than an Invar® mold. Therefore, CF composite molds have shorter heat up and cooling times, which allows for a faster cycle time in an oven or autoclave.
CF reinforced composite materials have been used to fabricate various sizes of lay-up molds. These molds are typically fabricated from either epoxy, bismaleimide (BMI), benzoxazine, or similar resins, which are reinforced with CF fabric, tape, chopped mat, or comparable material. The mold is then cured using heat and pressure. The so-produced molds are used in hand lay-up, tape laying, and fiber placement mold manufacturing processes. Such CF composite material lay-up molds are typically employed at, processing or curing temperatures ranging from about 250° F. to about 425° F., depending on the resin system used with the CF to make the composite part.
Where higher processing temperatures and high volume production runs are required, i.e., 350° F. or higher, such molds are usually manufactured or fabricated from either Invar® 36 or Invar® 42 iron-nickel alloys. Invar® 36 molds are useful at temperatures of up to about 550° F. while Invar® 42 molds are usually employed at temperatures of up to about 700° F.
Conventional Invar® molds, are usually formed from Invar® plate stock having an eggcrate shape or similar support structure configuration and a working surface. The plates used to fabricate the eggcrate support structure usually have a thickness ranging from about 0.25″ to about 0.50″. The final working surface of the mold, generally, is fabricated from plates having an initial thickness ranging from about 0.50″ to about a 1.0″ thickness.
After fabrication, the working surface of the plate stock is machined to the final configuration of the composite part that will be laid up on the mold. These Invar® molds have two to four times the weight of a CF composite material mold and, therefore, have a higher thermal mass requiring a longer heat up and cooling time.
The biggest advantage to an Invar® mold is its ability to be cycled an almost infinite number of times at temperatures ranging from about 350° to about 700° F., depending on the Invar® alloy, without requiring replacement. Contrariwise, a CF composite mold, when used at high temperatures, i.e., from about 250° F. to about 400° F., has a finite life of approximately 50 to 500 cycles, depending on the resin system and use temperature. When approaching the end life of the CF composite mold, the mold begins to degrade to a point where it must be replaced.
It is to be thus appreciated that if the respective advantageous properties of a CF composite mold and an Invar® mold could be integrated into a single mold then, clearly, an advantageous resultant product would be achieved.
The present invention, as detailed below, provides a mold which achieves this purpose.